Electromagnetic Interference with Aircraft Systems: why worry?

Peter B. Ladkin

Article RVS-J-97-03

Abstract: There are worries about suspected
electromagnetic interference with aircraft systems from electronic devices
used by passengers. Some first-hand incident reports from colleagues
are included. The phenomenon seems to be hard to pin down -- colleagues
explain why. It may be that the current regulatory situation affects
reporting and investigation of suspected incidents. Finally, I suggest some
ways in which the regulatory environment could be changed to aid
investigation.

Everybody knows how difficult listening to the radio or watching TV
becomes when someone is using the vacuum cleaner in the next room. The
vacuum cleaner causes significant interference with the radio signal.
I used to live in a house in Kensington, CA,
with an electric garage door opener, activated from the road
by a small radio device carried in my car. The door would occasionally open
by itself, early in the morning, on some rainy days when SFO was
using RWY 19 for arrivals, and the flight path came more-or-less overhead.
Now, there's an anecdote. I don't know it was aircraft transmissions;
I don't know it wasn't a passing taxicab whose driver was talking to base;
I don't even know it wasn't a fault in the door opening mechanism.
We may presume that the system was not very well shielded from
electromagnetic interference, and it is certainly not certified to
the same rigorous standards as avionics (`aviation electronics').

Nevertheless, there are similar worries in aviation at the moment.
Passengers use electronic devices on board aircraft, including some such as
cellular phones that they shouldn't in any case be attempting to use,
and pilots have reported anomalies with their navigation equipment that
seem to correlate with use of personal electronics in the cabin.
An overview of the technical issues may be found in
(Hel96).

There have been to my knowledge no reports so far of interference
with electronic flight control on the Airbus A320/330/340
series or the Boeing B777. These systems are shielded very well against
electronic signals, because they have to fly through radar beams and
other electromagnetic fields that may be occasionally very strong.
There is nevertheless some experience with electromagnetic interference with
electronic flight controls.
Five crashes of Blackhawk helicopters shortly after their
introduction into service in the late 1980's
were found to be due to electromagnetic
interference from very strong radar and radio transmitters with the
electronic flight control systems
(1).
So concern about this phenomenon is not purely the result of speculation.
It has actually happened, and it is appropriate
to be concerned about the possibility of similar phenomena in transport
aircraft.

Bruce Nordwall
(Nor96),
writing in
Aviation Week and Space Technology
in September 1996,
reported on the topic of an RTCA report to the FAA Administrator.
At the request of the FAA, RTCA Special Committee 177 was formed in
1992 to look into the possibility of interference with aircraft systems
from electronic devices operated by passengers during flight. Such devices
include laptop computers, Gameboys and, more insidiously, portable
personal telephones employing cellular technology.

Nordwall reported the RTCA advisory group to be worried that no group
was testing or systematically tracking the potential effect of
passenger electronics on avionics.
The group was also concerned that the flying public is not being educated
about the potential hazard, and that the airlines must largely figure out
how to deal with the issue themselves. Most airlines in the US already prohibit
use of passenger electronics of any sort below 10,000ft altitude.
There is most concern for the future; that rapid increases in the
technology of personal communications may allow passengers to bring
aboard with them, and inadvertently or surreptitiously use, devices
such as personal satellite phones that may be capable of significant
levels of electromagnetic radiation. The RTCA report recommends
developing and installing devices in aircraft cabins that could
detect and locate potentially harmful radiation coming from within
the aircraft. John Sheehan, the chairperson of RTCA SC-177,
kindly provided the Executive Summary of SC-177's report, RTCA DO-233
(RTCA96).
The Summary is included here as
Appendix A.

Navigation systems are particularly vulnerable for two reasons:

they have parts devised to detect and act on signals coming
from `outside';

radio-based systems are particularly susceptible to low levels
of interference.

Aircraft
control systems are located entirely within the aircraft and are shielded
from absolutely any signals not coming from one of their own devices;
they are also not radio-based, but are based entirely on electrical
signals conducted through wires as are most computer networks
(in the future, maybe also light signals conducted through glass-fibre cables).
Navigation avionics, on the other hand, must have some designed sensitivity to
environmental radio signals in order to perform their function.
Nordwall says

THe antennas of radio-based avionics may be affected by [electromagnetic]
field intensities of only microvolts per meter. But being outside the
aircraft, the antennas get some protective attenuation from the fuselage
of radiation originating inside the aircraft. Non-radio systems generally
have higher signal levels, and so are less susceptible to low levels of
interference.

The hull of a metal aircraft forms an effective
electromagnetic boundary between the outside and the inside of an
aircraft. Electromagnetic signals find it hard to get in, or to get out.
That is why the navigation and radio antennae on an aircraft need to be
placed outside the aircraft hull. But while outside they must be
sensitive, the navigation electronics inside the hull can be in principle just
as well and securely shielded as control avionics, because there is no
reason at all for navigation systems to be sensitive to electromagnetic
signals coming from inside the aircraft -- indeed, very good
reasons for these systems to be very insensitive, namely, that
there is lots of other electronics working there as well.

The Regulatory Environment

US Federal Aviation Regulation 91.21 prohibits the use of any portable
electronic devices on board aircraft, with the exception of voice recorders,
hearing aids, heart pacemakers, shavers, and any other device that
the operator of the aircraft has determined will not cause interference
with the navigation or communication systems of its aircraft:

91.21

Portable electronic devices

(a)

Except as provided in paragraph (b) of this section, no person
may operate, nor may any operator or pilot in command of an aircraft allow
the operation of, any portable electronic device on any of the
following U.S.-registered civil aircraft:

(1) Aircraft operated by a holder of an air carrier
operating certificate or an operating certificate; or

(2) Any other aircraft while it is operated under IFR.

(b)

Paragraph (a) of this section does not apply to--

(1)Portable voice recorders;

(2)Hearing aids;

(3)Heart pacemakers;

(4)Electric shavers; or

(5)Any other portable electronic device that the operator of the
aircraft has determined will not cause interference with the
navigation or communication system of the aircraft on
which it is to be used.

(c)

In the case of an aircraft operated by the holder of an air
carrier operating certificate or an operating certificate,
the determination required by paragraph (b)(5) of this section
shall be made by that operator of the aircraft on which the
particular device is to be used. In the case of other aircraft,
the determination may be made by the pilot in command or other
operator of the aircraft.

The regulation puts the responsibility firmly on an individual airline
to determine that there is no interference.
However, as Nordwall points out,
`Compact consumer electronic devices have proliferated in numbers
that defy cataloguing, let alone testing.'
The question is what would constitute an
appropriate `determination of no interference'.
In contrast to the US Federal Aviation Regulations, the International
Civial Aviation Organisation (ICAO) has no regulations relating to
portable electronics.

US airlines implement a general ban on using any portable electronic devices
(PEDs) below 10,000ft. According to former FAA associate administrator for
regulation and certification, Tony Broderick, this action was first
initiated by Northwest Airlines, and other airlines quickly followed
suit. Broderick notes that use of PEDs during takeoff and landing phases
is to be discouraged anyway, not only because of possible consequences
of EMI but also to encourage passengers to pay attention to the cabin
crew in case an emergency should arise during these critical phases
of flight
(Bro97)
(a commercial aircraft is below
10,000ft usually only during the takeoff and landing phases of flight,
and according to the Boeing statistics, 20.9% of all fatal accidents
to jet aircraft
have happened during takeoff and initial climb, and 46.6% during initial and
final approach and landing
(Boe96)).
Broderick also believes that the FAA, in cooperation with the industry,
will need to determine if there is indeed a problem with PEDs on board
aircraft, and that it will soon become commonplace to have PEDs on
board that are doing things (for example, transmitting)
that their owners aren't really aware of.

Some Issues Particular to Cellular Phones

Cellular phones, often
called Cellphones in the US and Handy's
in Germany, are a particular source of problems because, regardless of
whether they may interfere with aircraft systems, the technology on
which cellular telephones are based precludes their effective use on
aircraft. This applies to all cellular phones, including the analogue
technology in the US and the digital GSM technology in Europe. It may
be worthwhile first to explain the known problems associated
with attempted use of cellular phones while flying.

The technology of cellular phones is based on small local ground-based
reception areas called `cells'. A cellphone user is served by just
one cell, and when reaching the boundary of a cell, will be `handed over'
to another cell which (s)he is about to enter. The topology of coverage
is based on the assumption that the user is on or near the ground, and
it is a technical assumption on which the entire system is based that
a user will be within `sight' of just one cell except when nearing a
cell boundary. When
in an aircraft, however, a user is within radio `sight' of many cells,
simply because (s)he is way off the ground. An attempted call or reception
from an aircraft would activate
many if not all cells in the local area, which `breaks'
the technology -- it causes many transmission problems and the system is
disturbed. Therefore the various communication authorities, such as the
US Federal Communications Commission (FCC), ban the attempted use of
cellular phones while on board aircraft.
However, such attempted use is not ipso facto rendered dangerous. It
is technically inappropriate and antisocial, as well as mostly futile.

On Saturday 1 March 1997, German Transport Minister Matthias Wissmann
was reported in the German and international press
as wanting a fine and up to two years in jail for people
attempting use of cellular phones on board aircraft. He was reported as
saying that

In order to further increase air transport safety there will be new
regulations in the use of these dangerous things [...]
In future the use of electronic equipment by passengers in aircraft
will be banned. (Uhr97)

Herr Wissmann's comment mentions the danger of attempted cellphone
use. He therefore seems to be speaking about the possibility of interference
with aircraft systems, which if true is certainly dangerous, rather than
simply the problem that it causes the cellphone technology to malfunction.

While one may applaud Herr Wissmann's proactive stance in addressing
a potential hazard, one may also query the wisdom of publically declaring
aerial cellphone use to be dangerous in the absence of any concrete proof.
My colleague Prof. Dr. Klaus Brunnstein of the University of Hamburg,
who avidly follows various potential public computer risks, commented
that

[...] German law still forbids mobile communication (with specific exemptions)
[...]
It is interesting that airlines don't
specifically refer to this law when announcing that [attempted use of]
mobile telephones [is] not permitted on board. (Bru97)

Brunnstein is not aware of any concrete proof of electronic interference
on German aircraft, but reports that EUCARE has more than 60 pilot
reports of potential cases of interference, including some with
cellphones. He laments the anecdotal
nature of these cases, since one requirement for accurate `forensics',
as he aptly terms it, is verifiability of the source data.

General Worries on Interference

Nordwall reports that the RTCA Committee 177 inquiry found 137
`incidents' (pilot reports, anecdotes) reported either to them,
or to the FAA/NASA Aviation Safety Reporting System (ASRS) program,
or to the International Air Transport Association (IATA).
VOR reception
(2)
was affected in 111 incidents -- by far the most
common occurrence. From the 33 reports direct to RTCA, 21 incidents
related to laptop computers and only 2 to cellular phones. Navigation
systems were affected in 26 of those incidents; fuel systems, warning
lights and
propulsion reported one incident each. Rough correlation of suspect
with effect by turning the suspect
device on and off was found in 14 cases, on-off-on in 6 cases,
and no correlation in 13 cases.

Some Anecdotes and Discussion

Jim Irving is a colleague who
flies B737 aircraft for a major US carrier. He has an anecdote:

[...] One day departing Portland
Oregon we noted that the FMC [Flight Management Computer]
Map display showed a disagreement with the
"raw data" VOR position. Our training is such that we would normally
immediately switch over to "raw data" and assume the FMC was in error.

We would have done that except that it was a beautifully clear day and I
looked out the window and was able to determine that the FMC seemed to be
right on. I called back to the cabin and asked the flight attendants to
check for someone using a cell phone or computer. A few minutes later they
called back to say that a man had been using his cell phone and it was now
off. Strangely (?) our VOR and FMC map now agreed.

Later in the flight the flight attendants called back and said that they
had caught the man using his cell phone again but this time we had not
noticed any problems, perhaps because we were in cruise far from the ground
and not paying as much attention.(Irv97),

André Berger
(who also has a
homepage)
is a colleague who flies B737 aircraft for a major
European airline and who has had first-hand experience of some of these
incidents. While interference is not proven, he believes it gives
considerable cause for concern; and that while it may be difficult to
demonstrate the relationship using Brunnstein's `forensic' criterion,
this could be due to the fact that
the equipment needed to do so is not on board the aircraft
at the times the incidents occur.
Berger monitors the IATA confidential incident reports, and also
has some experience of his own to contribute:

In our company we recently had a Localizer deviation (out of tolerances)
on a B737-200 related to a GSM (mobile phone) being operated by a
passenger (who was disregarding our company regulations). When requested
by the cabin crew to switch off his GSM, localizer indications became
normal. Is this scientific proof? Certainly not, but good enough for me
as a captain to insist that all the electronic toys, computers, mobile
phones, etc., are OFF during critical phases of flight. [...]

I had fuel indications on the FMC going crazy on board the
B737, that returned to normal when all electronic stuff in the back
was switched off. I suspect a "Gameboy" electronic game device to have
interfered, but this is no more than a guess. No, I did not ask to
switch the toy back on again and investigate more in depth as I was
responsible for the safety of 140 passengers and this would have been
extremely irresponsible! This is not a situation in which to do such testing!
This [ever-present responsibility accounts for why]
there is no "proof" of the relationship.

I also recall experiencing *impossible* mode annunciations on the FMA
(flight mode annunciator) on B737. Having both the autothrottle AND the
pitch channel of the autopilot trying to maintain speed (both in MCP SPD
mode) for example, not programmed by the pilot (you cannot program
that). After an expensive in-depth troubleshooting session by our
maintenance department, the incompatible mode annunciations were traced
to a ... faulty cockpit window heat wiring. This caused electronic
interference with the auto flight system.(Ber97.1),

Berger has also recounted two more incidents:

June 07, 1997. B737-300:
*Verify position* was indicated on the CDU. Both IRS and radio position
were correct, the FMC position was not. The difference rapidly increased to
8 nautical miles. After switching a GSM in the cabin from STBY to OFF, the
FMC updated normally. FMC was correct for the remainder of the flight and
on the return flight.

April 30, 1997. B737-400:
During level cruise, the AP pitched up and down with ROC/ROD of 400 fpm
indicated. Other AP was selected: no change. Cabin was checked for PC's and
other electronic devices: nothing was found. Requested passengers to verify
that their mobile phone (GSM) was switched OFF. Soon after this request all
pitch oscillations stopped.

Just glitches or did interference really occur? Don't know, but EMI
(electro-magnetic interference) is a problem that needs more research.(Ber97.2),

Apparently, there are also some incidents with older aircraft. Here is
Berger's response to a query from another colleague:

> Has anyone heard of EMI incidents involving older Aircraft, i.e. 707,
> DC9,747-200, where system signal strengths are larger, and a lot more
> are analog?

[There was one incident reported with a] B737-200.
During approach to MAN (Manchester International, UK), the LOC for landing
runway 24 oscillated and centered with the aircraft not on track (but
offset), confirmed visually. Ground equipment was monitored and working
normally. When a GSM in the cabin was switched off, all indications became
correct.(Ber97.3),

Frank McCormick, an aerospace engineering colleague who is also a
FAA Designated Engineering Representative,
wonders about the physics of such possible incidents:

The threat levels presented by the gadgetry in question -- personal
computers, cellular phones, compact-disk players, hand-held video
games and so on -- are mere background noise compared to the threat
levels that must be demonstrated during environmental qualification
testing [of the aircraft systems].
How could an FMC [Flight Management Computer]
pass, say, DO-160C [standard certification] tests, yet lose its
mind in the presence of a cell phone on standby?(McC97),

and Peter Mellor, of the Center for Software Reliability at City University
in London, reports that

The cabling on the A320 has not only been tested for
resilience to "normal" EMI, but for its ability to withstand
the much greater pulse that would result from the aircraft
flying through a powerful radar beam, for example. (Mel97),

While doubting that the suspected-EMI phenomenon is ubiquitous,
McCormick suggests that some sort of systematic investigation could proceed
by inviting protagonists (actual airplane, pilots, customer with
suspect device) to participate in attempts to reproduce the incidents.
Berger reports that in fact very few systematic tests are performed
anyway: he asked a major portable phone manufacturer's representative
what tests they performed for EMI from their devices in aircraft.
The manufacturer performed none because use of cellphones is
illegal in aircraft. Berger notes that nevertheless such tests are
relevant, because these phones are frequently
used surreptitiously or inadvertently on aircraft.
He also notes that most electromagnetic interference testing is
`bench-testing', performed on independent subsystems, and that
this may suggest an interesting suspect point of weakness in the aircraft,
namely the system interconnections.
Recall one of the incidents he noted above: neither the electronics nor
the well-shielded wiring itself, but the wiring connections
seem to have been problematic.
He reports incidents to specific aircraft (whose registration `tail numbers'
are also given in the reports):

On a specific B737-300, a MCP (mode control panel) was doing weird stuff
intermittently during several flights. I mean really weird: like letting
both pitch and autothrottle fight each other to maintain speed. Nearly all
boxes involved (MCP, FCC, several AFDS boxes) were changed before a clever
mechanic found out that the windshield heat was not correctly grounded.
This is located just a few inches from the MCP and is one of the big
consumers on board. Tightening a few nuts solved an engineers nightmare.

On a specific B737-400, the FMC was doing weird things, mainly
in cruise. Some pilots reported that after a request to the passengers to
switch off electronic equipment, the problem was solved, others said it did
not help anything even with every electronic gadget switched off in the
cabin. Others reported nothing abnormal with CD's, PC's, Gameboys and more
of that stuff trying to jam the system unsuccessfully. Troubleshooting was
done and it was decided to replace another black box that was suspected. It
was pulled out but, no spare was available. So the same black box was
pushed in again. Problem solved, it never happened again!

Connections are a possible weak point. And difficult to duplicate if a
problem exists. Can an imperfect connection make a tested system EMI
susceptible or not?(Ber97.3),

He emphasises, as do the RTCA and the other correspondents, that more
research and systematic methods of testing are urgently to figure this
situation out.

John Dimtroff
is an electrical engineer on the Transport Standards Staff of the
FAA Transport Aircraft Certification Directorate in Seattle.
He is also a member of
the Joint Airworthiness Authority/Federal Aviation Administration
Electromagnetic Effects Harmonization Working Group. He has been
a Federal Communications Commission investigator and inspector, a Boeing
RF design engineer and a US Air Force Radar Specialist. Dimtroff
reports some incidents first-hand:

...even the aircraft's own certified airborne equipment
can play games on itself. [A few] years ago I was involved
in identifying the source of [navigation instrument indicator]
needle swings and voice modulations in the pilot's headset.
[The culprit turned out to be a]
certified airborne-authorized telephone
broadcasting on a frequency which just happened to be
commensurate with a piece of [navigation] equipment.

...my experience with the FCC has taught me [to wonder] how
many [PED] devices transmit with a clean, zero-spur signal,
especially after being dropped, banged, klunked, fondled and
sat upon. [In] my former FCC investigative days, [I saw] a number of
devices (computers, stereos, TV's, etc., etc.) which
purportedly met FCC Part 15 requirements as indicated by their
label, [but] were either bogus marked, illegally imported or were
just outside the manufacturing quality bell curve. [My personal view is]
that every carry-on electronic device is suspect -- until it
has been individually tested, which, of course, is impossible.

[My experience suggests to me that] it is nearly impossible to
predict/replicate an EMI event on an aircraft when the event
involves a portable carry-on device (PED). Location,
orientation, power output, modulation, inconjunction with ALL
the other PED's/electronics/electrics/avionics active at that
time all play a role in the EMI event. And we must not exclude
the terrestial based emitters (radars, etc). ...(Dim97),

ARSR Summary of Reports, 1986 - June 1994

The following summary prepared by the ASRS was forwarded by
Peter Mchugh
of the FAA's Office of Aviation Safety,
taken from Quick Response No. 271 dated November 30, 1994
(Mch97).

The following synoptic analysis of passenger electronic devices
incidents was accomplished by the ASRS staff [at the request of the
FAA]:

There were a total of 46 passenger electronic devices related
incidents in the ASRS data base covering the period Jan 1, 86 thru
June 30, 94. This number is in contrast to the 51,337 full form
reports covering all types of incidents reported to the ASRS during
the same period.

Passenger electronic devices incidents comprise .08 percent of
the
total full form reports in the ASRS database. Full form reports
receive full analysis processing and include the reporter's narrative
as part of the database record.

33 of the incidents referenced alleged aircraft systems interference
from an onboard passenger electronic device. 10 of the incidents
referenced alleged interference from an unknown onboard source. The
remaining 3 reports make reference to FAA policy about the use of
passenger electronic devices.

21 passenger electronic devices were specifically identified to be
the sources of the aircraft systems interference. The reporters noted
the interference ceased after the devices were turned off. The
identified passenger electronic devices included:

Cell phones (4)

Laptop computers (4)

Portable AM/FM Radio Cassette Players (4)

Portable CD Players (3)

Electronic Games (3)

HF Radio (1)

Heart Monitor (1)

One report cited interference from 23 passengers using AM/FM radio
cassette players.

Two reports cited passenger use of cell phone as a cause of dual
VOR nav failure.

None of the passenger electronic devices incidents had a critical
impact on the safety of the flight.

Mchugh urges caution in interpreting the data. It has limited
statistical significance because

reporting is voluntary and there is no statistical understanding of
the total reporting population or any way of estimating what
the actual number of events might be;

reporting is subjective and influenced by biases, including that
reporters gain protection from FAA regulation-enforcement procedures
and it is undoubtedly the case that some reports are generated
mainly for that reason, and this may affect the quality
of the report.(Mch97).

(Indeed, many private pilots I know, including myself, carry ASRS
reporting forms with us in our flight bags on every trip!)
Accepting these caveats, however,
the ASRS assembles many more anecdotes than
other systems, and Mchugh notes that it is in many cases the
"only game in town". And the personal, subjective nature of
the reports can provide insight into the human factors issues
resident in some events(Mch97).

Social and Administrative Pressures

The physical phenomenon of EMI interference seems to be relatively emphemeral.
It is hard to determine if specific incidents are examples of the phenomenon,
partly for the reasons Dimtroff remarks.
In this respect,
as McCormick points out, it distinguishes itself from other
recurring problems such as icing,
controlled flight into terrain (CFIT), and cargo-hold fire prevention and
detection. These latter problems have clear, undisputed
instances, and the question is what to do to prevent them.
The question with EMI is what kind of a problem it is, and how to
obtain clear instances.

There may be social and legislative pressures on
participants which may color their response to this situation.
Consider the following circumstance. US airlines
may only allow use of PEDs if they are known to the airline not to cause
interference (FAR 91.21). As we have noted, it is largely impractical to
submit devices to stringent test, considering the
number of devices on the market, and the varying condition of individual
devices. Suppose a US airline reports and investigates an incident, suspected
to be EMI. Ipso facto, that airline cannot therefore be deemed to have
`determined ... non-interference', as required by FAR 91.21. Just
the opposite, in fact -- they have suspected interference!
Therefore, FAR 91.21 prohibits use of such a device on board that aircraft.
A strict reading of the legislation thus leads directly from suspected-incident
report to prohibition on that airline.

However, other airlines permitting use of such devices could legally
continue to do so until they themselves were subject to an incident.
A US airline fastidious about reporting and pursuing
alleged EMI incidents could therefore find itself at a competitive
disadvantage as it must prohibit PED use,
and laptop and Gameboy users and cellphone owners with a
penchant for not turning their devices off might well
move their custom to rival airlines.
Thus may airlines find themselves in a situation in which they must
downplay reports or risk losing business, as a consequence of requirement
FAR 91.21.

In Europe, many aircraft and crews are certified for the demanding
automated approach procedures known as Category III (CAT III), in which
the autopilot, following navigation signals, flies the aircraft on landing
all the way to main gear touchdown on the runway.
A reported incident of suspected EMI with PEDs on board
such an airplane could seriously bring into question the aircraft's
CAT III certification, since the aircraft electronic systems must be
demonstrably highly reliable in order to exercise CAT III authority.
An airline reporting such incidents officially could suffer the loss
of CAT III certification on the incident airplane until the problem
is discovered and rectified. Since EMI incidents, as we have remarked,
appear to be very difficult to reproduce on the ground, one could imagine
a scenario in which an airline reporting a suspected EMI incident
is unable to trace the source, and therefore cannot exercise the CAT III
capability on that airplane again. This would be a serious service
limitation in the European environment. Again, this situation reveals
a potential competitive disadvantage to airlines which take suspected
EMI incident reports seriously.

If social pressures exist for airlines to downplay potential EMI
incidents, one could also foresee the possibility of pressure from airline
management on line pilots also to downplay observed avionics anomalies in
service. It is easy to see that both of these social pressures could
result in general underreporting and underinvestigating of
suspected EMI incidents.

Finally, the pilot in command is directly responsible for the safety
of those on board the aircraft. As André Berger has remarked,
this responsibility includes avoiding all potential safety
degradations, no matter how minimal. Thus, if EMI from a passenger
PED is suspected, the only appropriate recourse, according to this
legislative responsibility, is for the pilot to require the device
immediately be turned off completely. This precludes any kind of correlation
testing, benign or otherwise. However, recycling the device and trying
to reobserve the interference is the most obvious simple test one
can perform, and could be deemed benign in many circumstances.
A fastidious interpretation of regulations concerning pilot
responsibilities will, however, preclude it.

Since the current regulatory situation may thus unwittingly
discourage reporting and investigation of suspected EMI incidents,
there is a significant role for regulators to play in encouraging
both reporting and investigation of such phenomena.
I see five proactive ways for regulators to help:

in providing guidelines for, and allowing, if not encouraging,
in-flight impromptu tests by the flight crew if certain sorts of
benign influence from passenger electronics is suspected;

in providing guidelines for ground-based testing procedures in the wake
of such incidents, possibly involving also the suspect PED equipment
and its owner/user;

based on a classification of reports of the incidents,
in clarifying which kinds of incidents would be considered to
constitute a maintenance problem, and of which sort, and how those
kinds would be considered to alter the certification status of the
aircraft (particularly with regard to no-go and CAT III status).

The last of these measures, of course, could only be taken in a
regulatory environment
in which an absolute ban such as that in FAR 91.21 did not apply. The
question of just what such an environment could look like is the
topic of the first measure.

Conclusions

There are plentiful anecdotes of possible electromagnetic interference with
aircraft systems. While the systems are subjected to thorough bench-tests
under conditions of electromagnetic interference
to demonstrate adherence to certification
standards, there appears to be no systematic process for investigating
and attempting to reproduce in-flight incidents, although the
British Airways BASIS system, ASRS and EUCARE provide systematic logging
of such reports, as one presumes do individual airlines for internal use.

Possible explanations of the lack of reproducibility of such incidents
center on the environmental differences between the `bench tests' for
certification, in which individual subsystems are tested independently,
and the integrated aircraft environment. While entire aircraft are
also subjected to some testing during certification, there may be
individual differences between aircraft: if wiring connections are
susceptible to interference, for example, then aircraft with a longer
maintenance record may be more prone to interference incidents
than brand-new ones.

While there is considerable disagreement amongst experts as to whether
the phenomenon -- or phenomena -- are indeed cases of electromagnetic
interference from passenger electronic devices, the call for more
systematic testing appears to be unanimous. I have argued that some
change in the regulatory environment will help. Nevertheless
it appears clear that,
whatever one's view on the reality of the phenomenon, an increasing
number of reports on correlation will continue to appear at ASRS,
BASIS and EUCARE.

Acknowledgements

My grateful thanks to those with whom I have engaged in correspondence
on these issues, and who gave permission for me to quote them and
summarise their arguments in this article: André Berger,
Tony Broderick, Klaus Brunnstein, John Dimtroff, Jim Irving,
Frank McCormick, Peter Mchugh,
Peter Mellor, Werner Uhrig. May all our comments bear fruit.
Thanks in particular to John Sheehan, Chairman of RTCA SC-177,
for providing and giving us permission to reproduce
the Executive Summary of RTCA DO-233.

(2):
Very-high-frequency Omni-Range (VOR) beacons are still the standard mode
of en-route navigation in developed countries. Some non-precision
approach-to-landing procedures are also based on VOR. A VOR beacon is
a ground transmitter, which sends radio signals which enable an aircraft
to determine which magnetic radial it is on in
relation to the transmitter. A magnetic radial of, say, 137°
is a straight line emanating from the transmitter in a direction of
137° from magnetic north. Simple trigonometry tells us that
two VOR signals from different transmitters
are therefore sufficient for an aircraft to determine its exact 2-dimensional
position over the ground (modulo the inevitable local and systematic
errors, which are usually minor).
Back

In response to a FAA request, RTCA Special Committee 177 was formed in 1992
to investigate and determine the causes of the potential interference to
installed aircraft electrical and electronic systems from portable electronic
devices (PED) carried aboard aircraft by passengers. While a small list of
suspected incidents of such interference from PEDs had been generated over
time, interference from a PED could not be duplicated under controlled
conditions.

Government and industry personnel contributed their efforts to defining the
potential interference phenomena, devising test procedures for both PED and
aircraft and attempting to assess the risk potential from such interference
events. A variety of common consumer PEDs were tested for various of
spectral emissions in all modes of operation. This test procedure was
specially devised to reflect the unique PED/aircraft interface, borrowing
test methods from FCC, MIL Standard and RTCA DO-160C test procedures.
Similarly, test methods were devised to determine the path loss factors of
low level signals radiated within aircraft cabins. These procedures were
then used in determining the potentially interfering signal's path loss in a
variety of transport category aircraft. Finally, the susceptibility to
interference of installed avionics systems was tested and threshold levels
determined. After analysis, the above activity yielded the information
necessary to determine the probability of interference to aircraft systems
from PEDs.

The intent of these activities was to provide government agencies and
aircraft operators with the test methods needed to determine whether a
potential for interference exists for certain PEDs, aircraft and combinations
thereof.

This work of the special committee was not to exhaustively test combinations
of PEDs and aircraft systems for interference, however, sufficient data was
obtained to make provisional inferences regarding the probability of
interference from PEDs not designed to intentionally radiate electromagnetic
energy. Insufficient resources were available to investigate the effects of
intentional radiators.

Those findings indicated that the probability of interference to installed
aircraft systems from PED, singly or in multiples, is extremely slight.
However, the slight possibility of interference to aircraft navigation and
information systems during critical phases of flight, e.g., takeoff and
landing, should be viewed as potentially hazardous and an unacceptable risk
for aircraft involved in passenger carrying operations. Therefore, the
committee recommends that the use of PEDs be restricted during certain
critical phases of flight.

The rapid advance of personal communications technology has created the
potential for the inadvertent or surreptitious use of PEDs capable of
producing significant levels of electromagnetic radiation. Since SC-177 was
unable to test devices designed to be intentional radiators, these devices
remain an unknown quantity regarding interference potential. However, since
the proliferation of these devices may cause a new dimension in interference
potential for aircraft, recommendations are made to largely prohibit their
use and continue research into their characteristics. The use of detection
devices within the aircraft cabin designed to receive potentially harmful
interference from PEDs should be pursued as an additional means of minimizing
the possibility of interference from these devices.

a. The use of any PED is prohibited in aircraft during any critical
phase of flight.

b. The use of any PED designed to transmit electromagnetic energy is
prohibited in aircraft at all times until testing has been
conducted to ascertain its safe use.

2. PED testing efforts should be continued by the FAA, airline
industry, and consumer electronics and aircraft manufacturers to
expand the investigation of those devices for their potential to
interfere with aircraft systems. This effort should include
existing and new technology devices, such as satellite
communications, embedded communciations devices and two-way pagers.

3. A public awareness campaign should be initiated by the FAA, airline
industry and aircraft and consumer electronics manufacturers to
educate the flying public regarding the potential interference
hazards from PED, especially those designed as intentional radiators.

4. Government and industry should pursue research into the design and
feasibility of using devices designed to detect emissions that
produce electromagnetic interference from PEDs within aircraft
cabins.